1. Field of the Invention
The present invention relates to a quantum device including a quantum ring, a manufacturing method of the same and a controlling method of the same.
2. Description of the Related Art
Recently, studies of a quantum device as a promising candidate for future electronic and optoelectronic devices have been made. Most of these studies have been made on a quantum well, a quantum wire, and a quantum dot. A study on a quantum ring has been also made. For example, in Patent Document 3, a quantum ring with a ring diameter of 0.3 μm is proposed. However, if the application thereof to a quantum computer is considered, the quantum ring needs to be small to such an extent that a single carrier can be confined therein. As the size of the quantum ring becomes smaller, the quantum ring becomes more widely applicable.
Incidentally, even now, it is possible to fabricate a split-gate structure quantum ring with a diameter of approximately hundreds of nanometers on a two-dimensional electron gas. For example, in Non-Patent Document 2, a quantum ring fabricated by partial oxidation with lithography technology using an atomic force microscope (AFM) is described. However, such a quantum ring depends on the two-dimensional electron gas under the surface, and its quantum effect is small, so that its application range is narrow.
In Non-Patent Document 3, a method in which a quantum ring is fabricated by a method similar to that of a self-assembled semiconductor quantum dot is described. It is noted that in this method, after a very thin capping layer is formed, post annealing is performed. The size of a quantum ring obtained by this method is several times larger than the self-assembled semiconductor quantum dot, the spatial distribution is random, and the size fluctuation is larger. Hence, it is of little practical use.
On the other hand, in Patent Document 4, a method of forming a quantum dot in a desired size at a desired position with AFM lithography technology is described.
However, even if any of the prior arts is adopted or any of the prior arts is referred to, the quantum ring cannot be formed in the desired size at the desired position.
Moreover, various methods of forming a qubit (quantum bit) composing a quantum computer have been studied. Further, a nuclear spin is desirable as a candidate for the qubit. This is because its decoherence time is as long as 10−2 seconds to 108 seconds. Therefore, a nuclear spin qubit in a liquid state is studied (Non-Patent Document 7). In this document, it is described that in a solvent in which a molecule containing a number of atoms with a nuclear spin ½ (for example, 1H, 13C, 19 F, 15N, and 31P) is dissolved, nuclear magnetic resonance (NMR) is performed as the manipulation of a nuclear spin quantum computer. Each of the atoms with a nuclear spin ½ acts as a qubit. In a molecule, atoms in different sites differ in resonant frequency, so that each qubit can be independently manipulated. This technique makes quantum Fourier transform and factorization of a small prime number possible. However, a device in a liquid state is difficult to be scalable.
Hence, a nuclear spin qubit in a solid state is required. For example, in Non-Patent Document 8, a Si-based nuclear spin quantum computer is proposed. In the quantum computer, using a 31 P atom with a nuclear spin ½ in 28Si as a qubit, the nuclear spin is rotated by combining the application of an electrostatic field and a resonant radio frequency (rf). A quantum gate composed of two qubits is implemented by combining electrostatic gates on the neighboring 31P atoms and resonant radio frequencies.
However, in such a quantum computer, it is difficult to precisely manipulate electron clouds using the electrostatic gates. Further, it is extremely difficult to precisely place one nuclear spin atom in each qubit.
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